The isotopes of helium and argon were studied in fluid inclusions of minerals form corundum rocks with anomalous light oxygen isotope composition (Khitoostrov, Northern Karelia, Russia). Isotopic composition of argon shows that the atmospheric component of noble gases is missing. Th erefore, all previously proposed models of participation in the fluid of the surface melt waters of the high latitude glaciers are incorrect. It was established a regular decrease of the values of the ratios He/Ar and Ne/Ar from the host rocks to the center of the body with corundum rocks. This indicates that there was a transverse thermal gradient. It is established that the isotopic composition of helium is significantly different in the host rocks and in corundum ones, in addition, there is a trend of correlation of enrichment by light isotopes for helium and oxygen. This allowed us to propose and substantiate an endogenous mechanism of fractionation of isotopes of oxygen and other chemical elements by the mechanism of thermal diffusion. Geologically was justified existence of the cascading effect of the separation thermodiffusion cells, which lead to significant isotopic effects. Cascading is realized due to the "fluid pump", in which role are acting amphibolazing gabbro in the contact with corundum metasomatites. It is assumed that the mechanism is not specific for the case corundum metasomatic rocks, which are a special case of manifestation of such a scenario in processes involving endogenous fluid flows in thermogradient conditions.